Abstract: The ubiquitous human Epstein-Barr virus (EBV) has been shown to be linked to a wide range of human cancers which include Burkitt's lymphoma, nasopharyngeal carcinoma, Hodgkin's lymphoma, adult T-cell lymphomas and lymphoproliferative diseases in immunocompromised patients. In vitro, EBV can efficiently transform human primary B-cells in vitro resulting in continual proliferation of the infected primary B-cells into transformed lymphoblastoid cell lines (LCLs). The nascently transformed B-lymphocytes by EBV are strictly latent in that a select set of genes are expressed, one of which is Epstein-Barr nuclear antigen (EBNA)3C. EBNA3C has been shown to be essential for B cell transformation in vitro by genetic analysis of the virus. Over the last decade the functions associated with EBNA3C has linked this essential molecule to regulation of viral and cellular transcription through interaction with the transcription repressor CSL, Nm23-H1, the tumor suppressor molecule Rb and other cell cycle regulatory factors which include Cyclin A and Cyclin D1. This proposal will investigate the interactions of the essential EBV nuclear antigen 3C and the cellular factors E2F and c-Myc involved in regulation of cell proliferation, cell cycle, transcription, and signaling involved in maintenance of cellular homeostasis. The specific amino acids of these cellular targets c-Myc and E2F interacting with 3C will be explored and the functional relationships examined in terms of B cell transformation and immortalization. The post-translational modifications of c-Myc and E2F important for activation of their regulatory functions will also be fully investigated. Simultaneously, we will generate site specific recombinant EBNA3C molecules that are knocked out for the specific interactions within the EBV genome to determine their role in primary B cell transformation.